The Last of Us just came out on HBO Max. One episode every Sunday until March. I'm thinking it's to prevent people like me from getting a subscription for a month, binging the one show I want to see, then canceling.
Also because one of the best ways to become part of the zeitgeist is to force people to have time to talk about it, anticipate it, and generally stretch things out. You don't get the Lost/GOT/etc cultural phenomena nearly as strongly if you release them all at once.